Heat exchanger

ABSTRACT

A heat exchanger including a series of concentric chambers of circular cross-section through which a first fluid is adapted to flow and a plurality of conduits, disposed within the chambers, through which a second fluid is adapted to flow. The conduits having fins such that heat is exchanged between the first fluid and the second fluid by means of convection and conduction through the surfaces of the conduits and fins. The heat exchanger also including hoppers below the chambers to collect the solid particulate impurities as they separate from the first fluid while flowing through the chambers and a water bath which may be added to wash the impurities out of the first fluid.

United States Patent 1191 Kimmel 14 1 May 15, 1973 54 HEAT EXCHANGER Primary Examiner-Charles J. Myhre [75] Inventor: J. D. Kimmel, Houston, Tex. 1: 52:22;f yz g fifcggliz ggt Streule, Jr [73] Assignee: Thermotics, Inc., Houston, Tex. 221 Filed: June 21,1971 [57] ABSTRACT A heat exchan er includin a series of concentric [211 App! l54732 chambers of cii 'cular crosssection through which a first fluid is adapted to flow and a plurality of con- [52] U.S. Cl. ..165/ll9, 165/146, 209/144 duits, disposed within the chambers, through which a [51] Int. Cl ..F28b 19/00 second fluid is adapted to flow. The conduits having [58] Field of Search ..165/95, 84, 146, fins such that heat is exchanged between the first fluid 165/103, 140, 119; 209/144; 55/122 and the second fluid by means of convection and conduction through the surfaces of the conduits and fins. [56] References Cited The heat exchanger also including hoppers below the chambers to collect the solid particulate impurities as UNTED STATES PATENTS they separate from the first fluid while flowing through 3,534,812 10 1970 Sandri ..165/l46 x the chambers and a water bath which y he added to 2,475,025 7/1949 Huff ...165' 140 x wash the mp i out o t firs fluid 2,790,550 4/1957 Doyle et al. ..209/l44 1,226,379 511917 Riley ..165/l40 12 Claims, 3 Drawing Figures 1 HEAT EXCHANGER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to heat exchangers and pollution control equipment.

2. Description of the Prior Art The cleaning of fluids carrying solid impurities has been a source of invention for many years. Several de vices have been invented to provide for the transferring of heat from one stream of fluids to another stream of fluids while simultaneously removing the suspended solid impurities fron one of the fluid streams, such as shown in U. S. Pat. Nos. 321,541; 614,360; 1,912,381; 2,667,941; 2,761,526; 3,444,855; and 3,512,340. These devices have taken the form of heat exchangers with one fluid flowing through a bank of conduits and another fluid flowing over the bank of conduits such that, by conduction through the conduits and by convection, heat is exchanged between the two flowing fluids.

The prior art shows that such devices have proven valuable in the cleaning of blast furnace gases which are to be used later in another capacity. The gases erupting from such furnaces are very dirty and carry in suspension large amounts of fine particles that were blown through the furnace charge. By cooling these gases, the solid impurities can more easily be separated from the gases. This separation has been aided during the heat exchanging process by utilizing water spray to wash the gases thereby causing the gases to be cooled and humidified such as in US. Pat. Nos. 1,912,381; 3,435,593; 3,456,928; 3,505,788; and 3,512,340. Thus, the cooling process, together with the washing process, causes the solid impurities to be susceptible of separation from the gases and collect in the bottom of the heat exchangers.

Various problems have arisen in the use of the prior art devices. To obtain an adequate exchange of heat between the two fluids, large banks of conduits have been built to provide sufficient cooling surface. Because of the size of the ducts and the great difference between the temperature of the fluid as it enters the heat exchanger and the temperature as it leaves, the velocity of the fluid as it leaves the heat exchanger is less than when it entered thereby creating a turbulent and uneven flow of the fluid through the heat exchanger.

The older devices have either used very long banks of conduits or have used an intricate and complex design of fins attached to the conduits to obtain a sufficient exchange of heat during the time the fluid flows through the exchanger such as in US. Pat. Nos. 2,281,206; 2,322,341; and 2,905,447. Often these fins have been designed such that dust has collected on the fins thereby contaminating the fluid as it flows through the heat exchanger. Particularly, where the fluid is heavily laden with particulate impurities, the particulate matter collects on the heat exchanger elements decreasing the efficiency of the heat transfer and causing mechanical failure due to the increased weight built up on the ducts.

SUMMARY OF THE INVENTION According to the present invention, there is provided a heat exchanger which not only eliminates the large banks of conduits and the collection of dust on the fins,

but also permits the fluid to flow through the heat exchanger at a more controlled velocity.

The present invention has eliminated the structural defects of the prior art devices by separating the banks of conduits into a series of concentric annular chambers each having a different volume such that the fluid enters the largest chamber and leaves the smallest chamber. The decreasing size of the chambers permits a more controlled flow of the fluid through the heat exchanger since the fluid contracts as it cools thereby decreasing in volume as it passes through the chambers which correspondingly reduce in size. Since the heat exchanger is composed of several concentric annular chambers, the vertical height of the heat exchanger is considerably reduced over a structure having one vertical chamber.

The present invention describes a structure which permits a wide variance in the pressure and temperature of the fluid. inner annular chamber is composed of at least one substantially circular annular wall which is freely suspended within the heat exchanger. This permits the annular chambers to expand and contract in response to the pressure and/or temperature change of the fluid thereby minimizing mechanical failure within the system. The round chambers are less likely to be damaged by expansions and contractions due to temperature changes than polygonal shaped structures. Furthermore, it is better suited to high pressure operation than the usual square design.

This structure also aids in separating the solid particulate impurities from the fluid. The velocity of the impure fluid decreases within the heat exchanger permitting the larger particles to fall. The falling particles agglomerate with other particles during the fall thereby also separating from the fluid. The present invention aids this process. As the fluid passes through the concentric annular chambers, it must change directions by either flowing over or under one of the freely suspended annular walls composing the annular chambers. This forces the fluid to whip around the end of each of the suspended annular walls. The centrifugal force on the particles makes them separate from the fluid and be flung downward into the hoppers.

The structures described in the prior art had permitted the falling particles to settle on the heat exchanger elements thereby decreasing the heat transfer and causing mechanical failure. The present invention prohibits such collection. The conduits of the present invention have radial fins extending longitudinally along the outer longitudinal surface of the conduits so that the dust cannot deposit on the fins but must drop down into the collecting hoppers. The heat exchanger conduits have limited support and as the cooling fluid passes through the longitudinal sections and then changes direction at the ends of the conduits it causes the conduits to vibrate. This vibration prevents the falling particles from clinging to the heat exchanger elements.

Other objects and advantages of the invention will appear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS For a detailed description of a preferred embodiment of the invention, reference will now be made to the accompanying drawings wherein:

FIG. 1 is a front view of a heat exchanger embodying the invention with a partial sectional view taken at a plane parallel to the axis of the heat exchanger;

FIG. 2 is a top view of the heat exchanger of FIG. 1 taken at plane 2-2 indicated in FIG. 1; and

FIG. 3 is an isometric view of one embodiment of a heat exchange element for use in the heat exchanger shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the three figures, there is shown a vertical cylindrical and insulated outer wall having a conical roof 12 with an inlet 14 at its apex for the entry of a hot gas. A conical outer hopper 70 is connected at its larger diameter end to the bottom of the cylindrical outer wall 10 by means of a cylindrical neck 72. The cylindrical neck 72 has a series of equally spaced outlets 74. The outer hopper 70 has a valve 76 at its apex to permit the removal of impurities which have dropped from the hot gas into outer hopper 70. Valve 76 may be a rotating self sealing valve or a suitable valve to handle pressure, temperature, 'cor'rosion or abrasion.

The inlet 14 leads into the central chamber 60 formed by an insulated and innermost annular wall 50. The annular wall 50 is attached to the roof l2 and coincides with the inlet 14. The lower end of the annular wall 50 is suspended within the heat exchanger terminating short of entering the cylindrical neck 72 of the outer hopper 70.

An insulated and inner annular wall 30 disposed between the outer annular wall 10 and the innermost annular wall 50 creates an inner annular chamber 40 which is concentric to the central chamber 60 and an outer annular chamber which is concentric with both the central chamber 60 and the inner chamber 40. The lower end of the inner wall is connected to the larger diameter end of a conical inner hopper 35. The upper end of the inner wall 30 approaches, but terminates short of the conical roof 12. The largest diameter of inner hopper is the same as the diameter of the inner annular wall 30. The inner hopper 35 is supported within the neck 72 of the outer hopper 70. The inner hopper 35 has a valve 36 at its apex which permits the removal of any collected impurities by allowing them to drop into outer hopper 70. The angle of inclination of hoppers 35, 70 is greater than the angle of repose of the collected impurities so that the particles will slide down to the respective valves 36, 76.

The concentric annular chambers 60, 40, 20 decrease in volume respectively permitting a more controlled flow of the impure fluid through the heat exchanger. Since the fluid cools as it flows through the heat exchanger, and thereby contracts, its volume decreases. The correspondingly decreasing sizeof the annular chambers thereby tends to maintain the velocity of flow through the heat exchanger.

The shape of the chambers 20, 40, affords added advantages. Since the chambers 20, 40, 60 are concentric, the vertical height of the heat exchanger is considerably reduced as compared to a single vertical chamber. The round chambers 20, 40, 60 are also much more resistant to high pressures than polygonal shaped structures.

The structure described above permits a wide variance in the pressure and temperature of the hot fluids. Since each annular chamber 20, 40, 60 is partially composed of either annular wall 30 or 50, which are freely suspended within the heat exchanger, the annular chambers 20, 40, 60 can expand or contract in response to the pressure and/or temperature change of the fluid thereby minimizing mechanical failure.

The use of freely suspended walls 30, 50 also helps in the separation of the solid particulate impurities from the fluid. Normally, the particles are removed by causing the velocity of the hot fluid to decrease by cooling the fluid so as to make the solid particles fall to the bottom of the heat exchanger. In the present invention, as the fluid passes through the concentric annular chambers 20, 40, 60, the fluid must change directions by flowing under innermost annular wall 50 and over inner annular wall 30. This requires that the fluid whip around the end of each of the suspended annular walls 30, 50 creating a centrifugal force on the particles forcing them to separate from the fluid and be flung down into hoppers 35, 70.

A nozzle 62 may be placed in the upper end of the central chamber 60 to spray the incoming hot gas with water to aid in cooling and in humidifying the hot gas.

Heat exchange conduits 81 are disposed vertically within inner annular chamber 40 and outer annular chamber 20. Conduits are connected at their ends in series by couplings 82 located in the upper and lower portions of chambers 20, 40. In the preferred embodiment several banks of heat exchange conduits 80 are placed in chambers 20, 40. Chambers 20, 40 are divided into sections such as are shown in FIG. 2.

Each section dividing chambers 20, 40 contains a pair of banks of heat exchange elements 80, i.e. one bank being disposed in chamber 40 and the other bank being disposed in chamber 20. Since bank 22 and bank 42 as shown in FIG. 1 are typical, they will be described in detail. Banks 22, 42 are connected in series by coupling 84 which pass over the upper end of inner annular wall 30. An inlet conduit 16 which passes through the upper portion of the outer wall 10 is connected to bank 22, and an outlet conduit 18 which passes through the upper portion of the outer wall 10 and over the upper end of the inner wall 30 is connected to bank 42. Each pair of banks disposed in chambers 20, 40 have an inlet conduit carrying a cooling fluid from an outside source (not shown). The inlet conduit 16 carries a cooling fluid from this outside source and causes the fluid to flow through bank 22 and then into bank 42 by means of coupling 84. Then the cooling fluid flows from the bank 42 through outlet conduit 18 and back into the outside source where the cooling fluid is recooled for recycling through the system. New cooling fluid may be added to the system if the reservoir of the outside source becomes low.

To aid in the heat exchange relationship between the cooling fluid and the hot gas, radially extending fins 88 are disposed longitudinally on the outer surface of the heat exchange conduit 80, and extend in the direction of the movement of the gas. The fins 88 provide additional cooling surface over which the hot gas will flow. Fins 88 are straight fins without any curves thereby resisting the accumulation of dust and other particles making the heat exchange between the cooling fluid and the hot gas more efi'rcient. Couplings 82, 84 have no fins, thereby preventing any dust from collecting on them.

The present invention further resists the collection of the particles and dust on the heat exchange elements by vibrating the elements thereby preventing the particles from clinging. The conduits 80 have a limited support within the heat exchanger such that the passage of the cooling fluid within the conduits 80 and the passage of the hot impure fluid over the fins 88 tend to make the conduits 80 vibrate. This causes any dust depositing on the heat exchange elements to fall down into hoppers 35, 70.

In the operation of the heat exchanger, hot gas enters the heat exchanger through inlet 14 and flows into central chamber 60. In a preferred embodiment, water is sprayed on the hot gas by nozzle 62 thereby beginning the process of cooling and humidifying the hot gas.

Upon reversing direction of flow fromdownward to upward, solid particles are thrown down into hopper 35 by centrifugal force. As the gas flows upwardly through the first annular chamber 40, it begins to cool and its velocity decreases as a result of this velocity decrease, larger particles carried with the gas begin to drop out and agglomerate with other particles being carried by the impure gas thereby causing them to separate also and collect in the bottom of hopper 35. The vibration of the heat exchanger elements will also cause particles to fall into the hopper 35. These impurities are removed from hopper 35 by opening valve 36 and permitting these impurities to fall into hopper 70 where they remain until removed completely from the heat exchanger via valve 76. Due to the cooling of the gas, a pressure differential is available to force the particles collected in hopper 35 to. flow into hopper 70. This valve 36 could be adjusted to give a constant flow of the collected impurities into hopper 70 if such was desired.

The velocity of the hot gas causes the hot gas to flow down the central chamber 60, under the suspended innermost annular wall 50, and into the lower portion of the inner annular chamber 40. There the hot gas flows in a heat exchange relationship over heat exchange conduits 80 of bank 42 where the hot gas is cooled.

The hot gas flows up through the inner annular chamber 40, over the upper end of the inner armular wall 30, and flows into the upper portion of the outer annular I chamber 20. There the hot gas flows over heat exchange elements 80 in heat exchange relationship where the hot gas is further cooled. The smaller impuritiesseparate from the hot gas at this point and collect in the outer hopper 70. The volume of the outer annular chamber is smaller than that of the inner annular chamber 40 thereby tending to maintain the velocity of thecooled hot gas as it flows through the heat exchanger to increase the efficiency of the heat transfer rate in chambers 20, 40.

The cooled hot gas flows down through the outer annular chamber 20 and into the outer hopper 70.. Again,

impurities drop out of the cooled hot gas and collect in an inner annular duct surrounding the central duct,

an outer annular duct surrounding the inner annular duct,

said central duct, inner annular duct, and outer annular duct being serially connected,

a plurality of individual heat exchange elements joined in series and disposed in the inner annular duct and the outer annular duct, said elements being adapted to receive a cooling fluid, said cooling fluid being passed in heat exchange relationship with said hot fluid as said hot fluid passes through said inner annular duct and said outer annular duct,

said central duct being free of heat exchange elements,

said inner annular duct and said outer annular duct having volumetric dimensions which adjust the rate flow of said hot fluid thereby permitting maximum heat transfer between said hot fluid and said cooling fluid.

2. A heat exchanger according to claim 1, wherein said central duct includes a fluid spray over the first fluid passing through said ducts.

3. A heat exchanger according to claim 1, wherein said concentric annular ducts are formed by two cylindrical walls, at least one of which has one end freely suspended said heat exchanger permitting the free expansion and contraction of said annular ducts resulting from temperature and pressure changes.

4. A heat exchanger according to claim 1, wherein said heat exchange elements comprise vertical conduits having fins disposed on their external surface.

5. A heat exchanger according to claim 4, wherein said fins extend radially and longitudinally along the extemal surface of said conduits.

6. A heat exchanger according to claim 5, wherein said heat exchanger conduits have a limited support within said heat exchanger whereby the passage of the second fluid through said conduits and the passage of said first fluid over the tins of said conduits cause said heat exchange elements to vibrate so as to prevent the collection of any particles on said heat exchange elements.

7. A heat exchanger according to claim 1 wherein said exchanger includes an outer annular wall with a large hopper attached to its lower end to collect any solid particles released from said first fluid, said large hopper having an outlet for the removal of said solid particles.

8. A heat exchanger according to claim 7, wherein one of said cylindrical walls has an inner hopper disposed on the lower end of the wall, said inner hopper being suspended within said larger hopper, and said inner hopper having an outlet for the removal of said solid particles.

9. A heat exchanger according to claim 8, wherein the angle of inclination of said inner hopper and said large hopper pemiits a greater gravitational force on the collecting particles than any frictional force between the collecting particles and the side of the hopper thereby always permitting said particles to slide to the lowest point in the hopper.

10. A heat exchanger including:

a casing having an inlet and an outlet, said inlet and outlet being adapted as the entrance and exit for a hot fluid,

said inlet being located at the top of said casing so that said hot fluid will at first-flow in a downward direction, 1 v

a longitudinally extending central duct, said duct including a fluid spray for the hot fluid passing through said central duct,

an inner annular duct surrounding the central duct,

an outer annular duct surrounding the inner annular duct,

said central duct, inner annular duct, and outer annular duct being serially connected,

a plurality of conduits joined in series and disposed in the inner annular duct and the outer annular duct, said conduit having radial fins extending longitudinally of the external surface of said conduits, said conduits being adapted to receive a cooling fluid, said cooling fluid being passed in heat exchange relationship with said hot fluid as said hot fluid passes through the inner annular duct and the outer annular duct,

said central duct being free of conduits,

an outer hopper connected at its larger diameter end to the bottom of a wall surrounding said outer annular duct, said outer hopper having an upper outlet and a lower outlet, and

an inner hopper connected at its larger diameter end to the bottom of a wall surrounding said inner annular duct, said inner hopper having an outlet emptying into the outer hopper.

11. A heat exchanger including:

a vertical cylindrical outer wall,

a conical roof covering the top of said cylindrical outer wall, said roof having an inlet at its apex, an outer hopper connected at its larger diameter end to the bottom of said cylindrical outer wall, said outer hopper having an upper outlet and a lower outlet,

an intermediate cylindrical wall creating an outer annular chamber, said intermediate wall terminating short of said conical roof,

an inner hopper connected at its larger diameter end to the bottom of said intermediate cylindrical wall, said inner hopper having an outlet emptying into the outer hopper,

an innermost cylindrical wall creating an inner annular chamber and a central chamber, said innermost cylindrical wall being connected at its upper end to the conical roof and its lower end being suspended within the inner hopper,

said innermost wall, and said inner wall, and said outer wall being concentrically disposed,

a first bank of conduits disposed within the inner chamber and a second bank of conduits disposed within the outer chamber, said second bank being connected to receive a cooling fluid which has passed through said first bank,

radial fins extending longitudinally along the outer longitudinal surface of the conduits,

means for supplying said cooling fluid to said first bank of conduits, and

means for supplying a hot fluid having solid particles carried therewith to said inlet disposed in said conical roof, whereby said hot fluid flows through the inlet of the conical roof downward through the central chamber, said central chamber being free of conduits, into the inner hopper where the solid particles drop out, then around the lower end of the innermost wall and upward through the inner annular chamber, and around the upper end of the intermediate wall and downward through the outer annular chamber into the outer hopper where additional solid particles are dropped out, and then the hot fluid leaves the heat exchanger through the upper outlet.

12. A heat exchanger according to claim 11 further comprising a fluid spray means located within said central chamber whereby said hot fluid is contacted with a fluid spray. 

1. A heat exchanger including: a casing having an inlet and an outlet, said inlet and outlet being adapted as the entrance and exit for a hot fluid, said inlet being located at the top of said casing so that said hot fluid will first flow in a downward direction, a longitudinally extending central duct, an inner annular duct surrounding the central duct, an outer annular duct surrounding the inner annular duct, said central duct, inner annular duct, and outer annular duct being serially connected, a plurality of individual heat exchange elements joined in series and disposed in the inner annular duct and the outer annular duct, said elements being adapted to receive a cooling fluid, said cooling fluid being passed in heat exchange relationship with said hot fluid as said hot fluid passes through said inner annular duct and said outer annular duct, said central duct being free of heat exchange elements, said inner annular duct and said outer annular duct having volumetric dimensions which adjust the rate flow of said hot fluid thereby permitting maximum heat transfer between said hot fluid and said cooling fluid.
 2. A heat exchanger according to claim 1, wherein said central duct includes a fluid spray over the first fluid passing through said ducts.
 3. A heat exchanger according to claim 1, wherein said concentric annular ducts are formed by two cylindrical walls, at least one of which has one end freely suspended within said heat exchanger permitting the free expansion and contraction of said annular ducts resulting from temperature and pressure changes.
 4. A heat exchanger according to claim 1, wherein said heat exchange elements comprise vertical conduits having fins disposed on their external surface.
 5. A heat exchanger according to claim 4, wherein said fins extend radially and longitudinally along the external surface of said conduits.
 6. A heat exchanger according to claim 5, wherein said heat exchanger conduits have a limited support within said heat exchanger whereby the passage of the second fluid through said conduIts and the passage of said first fluid over the fins of said conduits cause said heat exchange elements to vibrate so as to prevent the collection of any particles on said heat exchange elements.
 7. A heat exchanger according to claim 1 wherein said exchanger includes an outer annular wall with a large hopper attached to its lower end to collect any solid particles released from said first fluid, said large hopper having an outlet for the removal of said solid particles.
 8. A heat exchanger according to claim 7, wherein one of said cylindrical walls has an inner hopper disposed on the lower end of the wall, said inner hopper being suspended within said larger hopper, and said inner hopper having an outlet for the removal of said solid particles.
 9. A heat exchanger according to claim 8, wherein the angle of inclination of said inner hopper and said large hopper permits a greater gravitational force on the collecting particles than any frictional force between the collecting particles and the side of the hopper thereby always permitting said particles to slide to the lowest point in the hopper.
 10. A heat exchanger including: a casing having an inlet and an outlet, said inlet and outlet being adapted as the entrance and exit for a hot fluid, said inlet being located at the top of said casing so that said hot fluid will at first flow in a downward direction, a longitudinally extending central duct, said duct including a fluid spray for the hot fluid passing through said central duct, an inner annular duct surrounding the central duct, an outer annular duct surrounding the inner annular duct, said central duct, inner annular duct, and outer annular duct being serially connected, a plurality of conduits joined in series and disposed in the inner annular duct and the outer annular duct, said conduit having radial fins extending longitudinally of the external surface of said conduits, said conduits being adapted to receive a cooling fluid, said cooling fluid being passed in heat exchange relationship with said hot fluid as said hot fluid passes through the inner annular duct and the outer annular duct, said central duct being free of conduits, an outer hopper connected at its larger diameter end to the bottom of a wall surrounding said outer annular duct, said outer hopper having an upper outlet and a lower outlet, and an inner hopper connected at its larger diameter end to the bottom of a wall surrounding said inner annular duct, said inner hopper having an outlet emptying into the outer hopper.
 11. A heat exchanger including: a vertical cylindrical outer wall, a conical roof covering the top of said cylindrical outer wall, said roof having an inlet at its apex, an outer hopper connected at its larger diameter end to the bottom of said cylindrical outer wall, said outer hopper having an upper outlet and a lower outlet, an intermediate cylindrical wall creating an outer annular chamber, said intermediate wall terminating short of said conical roof, an inner hopper connected at its larger diameter end to the bottom of said intermediate cylindrical wall, said inner hopper having an outlet emptying into the outer hopper, an innermost cylindrical wall creating an inner annular chamber and a central chamber, said innermost cylindrical wall being connected at its upper end to the conical roof and its lower end being suspended within the inner hopper, said innermost wall, and said inner wall, and said outer wall being concentrically disposed, a first bank of conduits disposed within the inner chamber and a second bank of conduits disposed within the outer chamber, said second bank being connected to receive a cooling fluid which has passed through said first bank, radial fins extending longitudinally along the outer longitudinal surface of the conduits, means for supplying said cooling fluid to said first bank of conduits, and means for supplying a hot fluid havIng solid particles carried therewith to said inlet disposed in said conical roof, whereby said hot fluid flows through the inlet of the conical roof downward through the central chamber, said central chamber being free of conduits, into the inner hopper where the solid particles drop out, then around the lower end of the innermost wall and upward through the inner annular chamber, and around the upper end of the intermediate wall and downward through the outer annular chamber into the outer hopper where additional solid particles are dropped out, and then the hot fluid leaves the heat exchanger through the upper outlet.
 12. A heat exchanger according to claim 11 further comprising a fluid spray means located within said central chamber whereby said hot fluid is contacted with a fluid spray. 